Reactions of (pentamethylcyclopentadienyl)(2,5-dimethylthiophene)iridium with iron carbonyls: a new mechanism for thiophene hydrodesulfurization

Abstract

Reactions of the isomers Cp*Ir(η 4 -2,5-Me 2 T) (1) and Cp*Ir((C,S-2,5-Me 2 T) (2), where Cp*=η 5 -C 5 Me 5 and 2,5-Me 2 T=2,5-dimethylthiophene, with iron carbonyls (Fe(CO) 5 , Fe 2 (CO) 9 , and Fe 3 (CO) 12 ) give eight different products, 3-10. Two of them, Cp*Ir(η 4 -2,5-Me 2 T•Fe(CO) 4 ) (3) and Cp*Ir(η 4 -2,5-Me 2 T•Fe 2 (CO) 7 ) (7), retain the η 4 -2,5-Me 2 T coordination to the Ir but are also bonded through the sulfur to the Fe atom(s). Both 1 and 2 react with Fe 3 (CO) 12 to give 8 in which all of the elements of 2,5-Me 2 T are present but the sulfur has been removed from the thiophene ring. Reaction of 8 with CO (1 atm) gives the totally desulfurized 9. A new mechanism is proposed for thiophene hydrodesulfurization (HDS) based on the C−S bond cleavage reactions which occur when 1 rearranges to 2 and 2 is converted to 8